Mrapen eternal flame is located in Manggarmas village, Godong, Grobogan, Grobogan regency. This geology phenomenon is flame that appears from the earth surface and never goes out, even in rainy season. The flame has been used for national sport event, and Buddhist too the flame as holy flame every vesak at Borobudur Temple.
Not far from the flame location, located batu bobot. Batu bobot is rock located inside a building with roof and locked. Local people believe that the rock can grant any request for anyone that can lift it. The stone is considered as sacred that it is poured with flowers.
Beside batu bobot, there is a pond with green water that is bubbling, looks like it is boiling. But the water is not hot as the bubbles come from gas under the surface. This pond is a spring called as Sendang Dudo, that contains calcium, magnesium and other minerals. As it is rich or minerals, the water can sure skin disease.
According to legend, the flame appeared after Sunan Kalijaga stick his cane. Sunan Kalijaga and his followers were on a very long journey, and stayed overnight at Mrapen village. His followers were feeling cold, so he stick his cane into the ground and then lifted again, and there the flame appeared miraculously and warmed them. Mrapen derived from prapen or fireplace, so the flame was called as Merapen. Another day, Sunan Kalijaga asked Mpu Supa, who lived not far from Sendang (Spring) Dudo, to make kris. Sunan Kalijaga gave Mpu Supa the material, iron ore with hazelnut size. Mpu Supa laughed, as it was impossible to make Kris with that small iron ore. Well, it seemed that he forgot that he was dealing with Sunan Kalijaga, a powerful man. The small iron ore expanded bigger and bigger as put on fire and he forged it. He brought the iron to Sendang Dudo and plugged the iron in. As the hot iron plugged to the water, the calm water turned to boiling water and turbid. The kris was named as Kiai Sengkelat.